Here are the steps to determine the actual elemental composition by weight of a fertilizer labeled 48-72-31: - 48% is the actual nitrogen (N) content since N is expressed as a percentage. - 72% is the P2O5 content. To determine the actual P content: - P2O5 is 43.6% P - So P = 0.436 x 72% = 31.5% - 31% is the K2O content. To determine the actual K content: - K2O is 83% K - So K = 0.83 x 31% = 25.7% Therefore, the actual elemental composition by weight of a fertilizer labeled

1. Nutrition

2. Nutrition
• Supplying nutrients to greenhouse crops is an exact process
• supply all the necessary plant nutrients with little margin for error
• A number of variables must be considered when developing a
fertilization program for a crop species
 Total quantity or application rates
 Proportions of each element
 Application method
 Interactions with:
media type
pH and EC level
 light levels
water quality
watering practices
production temperatures

3. • One other point to consider is the method for expressing the
concentrations of (N), (P), and (K) in a fertilizer
 Nitrogen is expressed as the actual percentage of nitrogen in the fertilizer
 Phosphorus is expressed as percentage phosphorous pentoxide (P2O5)
only 43.6% actual phosphorus
 Potassium as the percentage of potassium oxide (K2O)
only 83% actual potassium
Nutrition

4. Essential Elements
• Essential elements are those elements required by plants to complete their
growth cycle
 Carbon, hydrogen, and oxygen comprise the backbone of all organic matter and
are supplied by (CO2) and (H2O)
 Although C, H, and O are not considered fertilizers, a crop is sometimes “fertilized” with
carbon through supplementary CO2
Primary Macronutrients
 (N), (P), and (K) – are supplied by most complete fertilizers
 Secondary Macronutrients
 (Ca), (Mg), and sulfur (S)
 used in relatively large amounts but not to the same degree as N, P, and K
 Most premixed fertilizers contain the SMs
Micronutrients(trace elements)
 (Fe), (Mn), (Zn), (Cu), (B), (M0), (Ni), and (Cl)
 Micronutrients can also be found in significant amount in water, some
fertilizers, media (especially those with soil), and fungicides
 Be careful when applying micronutrients, as the difference between
deficiency and toxicity is often small

5. Nitrogen (N)
• Two forms of nitrogen important in plant growth are ammonium (NH4)
and nitrate (NO3)
 The common fertilizer urea [Co (NH2) 2] is considered an ammonium fertilizer in
that it releases amides (NH2
+) which are converted to ammonium either in the
medium by microorganisms or within the plant
 Most plant species grow best when both nitrate and ammonium forms of
nitrogen are supplied
 Sources of nitrogen are various and are commonly available in the form of:
Potassium Nitrate (KNO3)
Calcium Nitrate [Ca(NO3)2]
Ammonium Nitrate (NH4NO3)
Urea [CO(NH2)2]
Diammonium Phosphate (DAP) [(NH4)2HOP4]
Sodium Nitrate (NaNO3)
Nitric Acid Liquid (HNO3), used to lower water pH and alkalinity and

6. Phosphorus (P)
• Phosphorus is required in the least amount of the three macronutrients,
usually 50% or less of N or K rates
• Phosphorus tends to be relatively immobile in soil-based media, but is readily
leached in soilless media, especially under high leaching (irrigation) rates and
low pH
 An interesting relationship exists between mycorrhizae fungi and P
 Excess P may accentuate Fe, Cu, or Zn deficiency and suppresses mycorrhizae
growth
• Phosphorus is available in various formulations
 Triple superphosphate [CaH4(PO4)2] (TSP)-low solubility, neutral, and most
commonly used as a preplant medium amendment
 Single superphosphate [Ca2H(PO4)2]- low solubility, neutral, also contains gypsum
(CaSO4) which supplies sulfur
 Monoammonium phosphate (NH4H2PO4)-soluble and acidic
 Diammonium phosphate (DAP)[(NH4)2HPO4]-soluble and acidic
 Phosphoric acid (H3PO4)-liquid, acidic, and used to lower water pH and alkalinity

7. Potassium
• Compared to nitrogen, potassium is found in plant material in
the same or slightly lower level
 both nutrients are usually supplied in similar amounts
 Excess K may accentuate N, Ca, or Mg deficiency
• Sources of this element could be:
– Potassium nitrate (KNO3)-soluble, basic, and the preferred fertilizer
because it supplies both K and N
– Potassium chloride (KCI)-soluble and neutral
– Potassium sulfate (K2SO4)-soluble and neutral

8. Calcium
• Calcium is a relatively immobile element that is transported by the
movement of water through the transpiration process
– Calcium deficiency can be accentuated by high Mg levels and low media pH
which allows faster leaching of calcium from the medium
– High levels of ammonium may reduce calcium uptake
– Excess Ca may accentuate magnesium (Mg) or boron (B) deficiency
• Sources
– Dolomitic limestone (CaCO3 + MgCO3)-low solubility, commonly used as a
preplant fertilizer to raise media pH, and the preferred source of calcium
because it contains both Ca and Mg
– Calcitic limestone “(CaCO3)-low solubility and will raise media pH
– Gypsum (CaSO4)-low solubility, neutral and used when media pH is not to
be increased
– Calcium nitrate [Ca (NO3)2]-soluble, basic, and commonly used in premixed
fertilizers
– Irrigation water in many areas may contain high levels of calcium, especially
water that has high alkalinity

9. Magnesium
• Magnesium and calcium are often considered together as both are strongly
antagonistic with each other in the root medium
 High levels of one element can induce a deficiency of the other
 recommended a general ration of 3 to 5:1 Ca: Mg in irrigation water and media
 Excess Mg may accentuate Ca or K deficiency
• Sources
 Dolomitic limestone (CaCO3 + MgCO3)-low solubility, frequently used as a preplant
fertilizer to raise media pH, and contains both Ca and Mg
 Magnesium sulfate (Epsom salts) (MgSO4 7H2O)-high solubility and neutral
 Magnesium ammonium phosphate (MagAmp®) (KmgPO4 + NH4MgPO4)-low
solubility and basic
 Magnesium oxide (MgO)-low solubility and neutral
 Magnesium nitrate [Mg (NO3)3 6H2O]-soluble and basic
 Irrigation water in many areas may contain high levels of magnesium, especially
water that has high alkalinity

10. Sulfur
• Sulfur deficiency rarely occurs due to the presence of sulfates in many
fertilizers
• Excess S may accentuate K, Ca or Mg deficiency
• Sources
– Gypsum (CaSO4)-low solubility, neutral and used when media pH is not to be
increased
– Single (mono) superphosphate [CaH(PO4)2]-low solubility, neutral, and contains
gypsum (CaSO4)
– Potassium sulfate (KSO4)-soluble and acidic
– Magnesium sulfate (MgSO47H2O)-soluble and acidic
– Ammonium sulfate [(NH4)2 SO4]
– Iron sulfate (FeSO47H2O)
– Aluminum sulfate [Al2(SO4)3]
– Sulfuric acid (H2SO4)-liquid, acidic, and used to reduce water pH and alkalinity

11. Iron (Fe)
• Iron is one of the most common deficiency problems in greenhouse production
• Iron deficiency is often due to high media pH (check media pH before applying )
• Excess Fe may induces iron toxicity and Mn deficiency
• Sources
– Iron sulfate (FeSO47H2O) - Iron chelates and most commercial micronutrient
• Excess Mn can induce Fe or Mo deficiency
• Sources
• Manganese sulfate (MnSO4 H2O), Manganese chelates, and most
commercial micronutrient
Manganese (Mn)

12. Zinc (Zn)
• Zinc is an active component of some fungicides, which may inflate Zn levels in
tissue tests
• Excess Zn may accentuate Mn or Fe deficiency
• Sources
– Zinc sulfate (ZnSO4:H2O), Zinc chelates and most commercial micronutrient
Cooper (Cu)
• Copper is also an active component of some pesticides which may
inflate Cu levels in tissue tests
• Excess Cu may accentuate Fe, Mn or Zn deficiency
• Sources
 Copper sulfate (CuSO4:5H2O), Copper chelates

13. • Water in some areas of the world can contain high levels of boron and can induce boron
toxicity
• Be sure to have water checked
• If a deficiency is noted, however, apply boron carefully as the difference between
deficiency and toxicity is especially narrow for this element
• Sources
• Sodium tetraborate (borax) (NaB4O7 10H2O)
• Boric acid (H3BO3), and most commercial micronutrient mixes
Boron (B)

14. Molybdenum (Mo)
• Molybdenum is rarely a problem
• Excess Mo may accentuate Cu deficiency
• Known sources are
 Sodium molybdate (Na2MoO4 2H2O)
 Ammonium molybdate [(NH4)2MoO4]
• Nickel and chlorine are required in minute amounts and
deficiencies do not occur in floriculture production
• Fertilizer and media have nickel and chlorine contaminants so
additional sources are not needed
Nickel and Chlorine

15. Fertilizer Application
• Of the 12 nutrients required by plants, firms must decide
whether to apply the nutrients :
 By incorporation into media prior to planting, and/or
 through fertigation system after planting, or
 a combination of both
Preplant Fertilization
• in corporation into media by:
• various controlled release fertilizers intended to last for the entire crop
cycle, or
• small amounts of soluble fertilizers intended to serve only as a short-
duration starter fertilizer

16. I. Controlled-release fertilizers (CRF)
• Controlled-release fertilizers have advantages and disadvantages
Advantages
 potentially reducing labor costs and
 reducing the waste of nutrients through leaching
 are more nutrient efficient than fertigation as more of the nutrients are
absorbed by the plant as opposed to being leached
 low amount to remain in the store
disadvantage
 grower loses control particularly for manipulating nutrients
 Most controlled-release fertilizers are temperature dependent and nutrient
release decreases when the temperature is cool
 high cost compared with constant liquid fertilization (CLF)
 difficulty of obtaining an accurate media test when controlled-release
fertilizers are incorporated into media

17. • In some cases, a grower might incorporate a slow-release
fertilizer into the substrate at half the recommended rate and
supply the remaining fertility requirement through a liquid
fertilization program
 This provides increased flexibility since once a slow-release fertilizer is
incorporated into a substrate it can't be removed and excess nutrients
can't be leached out
Controlled-release fertilizers….

18. Types of Controlled-Release Fertilizer
 This includes fertilizers such as limestone, gypsum, and superphosphate
 Slowly soluble fertilizers release nutrients by dissolving (increasing
moisture increases the release rate)
 The more finely the material, the faster the release rate
 Increasing temperature increases the release rate
 Low media pH will allow limestone to dissolve quicker
I. Slowly soluble

19.  This includes Osmocote®, Nutricote®, Precise®, and others
 The hydroscopic fertilizer attracts water through pores in the plastic coat,
expanding the capsule and allowing the concentrated fertilizer-water
solution to be released
 The release rate is controlled by the pore size and thickness of the plastic coat
 Longevity of the CRF is specified by the manufacturer and varies from 3 to 14
months
 Release rates also vary among the different manufactures depending on the
composition of the coating
 Temperature increases release rate (average medium temperature of 210C)
 Plastic-coated fertilizers cannot be heat pasteurized as that will affect the
coating
 The moisture level between container capacity and the permanent wilting
point will not affect the release rate
Types of Controlled-Release Fertilizer…
2. Plastic coated

20. II. Constant Liquid Fertilization (CLF)
• It is the application of water-soluble fertilizers through the
irrigation water
 Liquid fertilization is most common with greenhouse crops
 Typically nutrients are applied at every irrigation when the plants
are actively growing
 Plants that are actively growing and drying quickly are more frequently
irrigated and fertilized. Similarly, plants that are growing slowly use less
water and fertilizer and are less frequently fertigated
 The fertilizer concentration depends on the species being grown the
irrigation frequency, and the leaching fraction
Fertigation

21. Reading and Understanding Fertilizer Labels
 In order to prepare fertilizer solutions or properly apply a fertilizer,
or to effectively use a fertilizer, the information on the label needs
to be understood
 Fertilizer labels contain a great deal of valuable information
 NPK rating (or N-P-K) is used to label fertilizer based on the relative
content of the Nitrogen (N), Phosphorus (P), & Potassium (K)
 Except for the N number, the numbers for P and K do not reflect the amount
of phosphorus and potassium in the fertilizer. Rather they represent the
amount of oxide in the form of P2O5 and K2O that would form if all the
elemental phosphorus and potassium were oxidized into this form
For instance a fertilizer label lists the % by weight of N, P2O5 and K2O.
Therefore, a 20-20-20 is 20% N, 20% P2O5 and 20% K2O.

22. Method for converting N-P-K value to an actual composition
• The factors for converting from P2O5 and K2O values to their
respective P and K elemental values are as follows:
– P2O5 consists of 57.4% oxygen and 43.6% elemental phosphorus
– The percentage [mass fraction] of elemental phosphorus is 43.6%
so P= 0.43 x P2O5
– K2O consists of 17% oxygen and 83% elemental potassium
– The percentage (mass fraction) of elemental potassium is 83% so K
= 0.83 x K2O
– Nitrogen values represent actual nitrogen content so these
numbers do not need to be converted
•

23. Rules for mixing fertilizers
• The first rule in mixing fertilizers is to always use high quality,
water soluble "greenhouse grade" fertilizers
• Never mix calcium containing fertilizers (e.g. calcium nitrate) with
any fertilizers containing phosphates (e.g. mono-potassium
phosphate) or sulfates (e.g. potassium sulfate, magnesium sulfate)
• When fertilizers containing calcium, phosphates or sulfates are mixed
together as concentrates the result is insoluble precipitates of calcium
phosphates and calcium sulfates
• Dissolve the fertilizers for each tank in hot water
– The micronutrients are added to the tanks when the solution is warm, not
hot
– Continually agitate the solution in the stock tanks as the fertilizers are being
added

24. Assignment
• Using the conversion factors determine how much
contains by weight a fertilizer labeled as 48−72−31